Powder coating compositions

ABSTRACT

The present invention relates to powdered thermosetting coating compositions comprising a co-reactable mixture of a glycidyl group containing acrylic copolymer, a carboxylic acid group containing acrylic copolymer, a carboxylic acid group containing polyester, all 3 compounds having a high Tg, along with a low Tg counter part 1 to 3 of these compounds, and a thermosetting catalyst. These thermosetting powder coatings particularly are designed for coating heat-sensitive substrates and produce a finish which exhibits reduced gloss.

The present invention relates to powdered thermosetting coatingcompositions comprising a co-reactable mixture of a glycidyl groupcontaining acrylic copolymer, a carboxylic acid group containing acryliccopolymer, a carboxylic acid group containing polyester and athermosetting catalyst. These thermosetting powder coatings particularlyare designed for coating heat-sensitive substrates such as wood,fibreboard and other materials, which can not withstand the excessiveheat/time conditions necessary to cure traditional coatings. The powdercoatings accordingly the present invention produce a finish whichexhibits reduced gloss, in the range of low to medium, along with anoutstanding surface aspect, hardness and weatherability.

Powder coatings which are dry, finely divided, free flowing, solidmaterials at room temperature, have gained popularity in recent yearsover liquid coatings. Despite their many advantages, nowadaysthermosetting powder coatings generally are cured at temperatures of atleast 140° C. Below this recommended temperature the coatings have poorappearance, as well as poor physical and chemical properties. Inconsequence of this restriction powder coatings are generally notemployed in coating heat-sensitive substrates. Recently there has been agood deal of effort in finding powder coatings for heat-sensitivesubstrates such as wood, fibreboards and plastic. A significantpotential for powder coating is wooden and fibreboard cabinet doors suchas those commonly used in kitchens and bathrooms. The coating for thisapplication must be both extremely durable because of heavy usage andweatherable because these surfaces are exposed to UV light which tendsto cause the finish to yellow. Further for aesthetic purposes a reducedgloss (60° gloss in the range of 5 to 50 according to ASTM D523) finishis highly desired.

Compositions that are today useful for heat-sensitive substrates andwhich provide a low gloss finish, are generally based on Bisphenol Aepoxies. However these compositions do not provide the UV stability thatis required for certain applications, such as for example kitchencabinets having a white surface finish. Over time, with exposure tosunlight, the surface finishes made from Bisphenol A epoxies will fadeor yellow out. Accordingly, it is an object of the present invention toprovide a low temperature curable powder coating which, upon applicationand curing, provides smooth finishes exhibiting a reduced gloss and aresistance to weathering.

Powder coating compositions comprising a glycidyl group containingacrylic copolymer and a carboxylic acid group containing acryliccopolymer and/or a carboxylic acid group containing polyester, and whichare intended, upon application on metal and heat-sensitive substratesand curing at conventional or low temperatures, for high gloss andreduced gloss coatings, already are subject to a certain number ofpatent(s) (applications).

For example WO 01/92367 claims for powder coating compositionscomprising from 10 to 90% weight of a carboxylic acid group containingacrylic copolymer and from 90 to 10% weight of a polyepoxy resin and acatalyst. Any type of polyepoxy resin can be used as such or in amixture with other crystalline or non-crystalline polyepoxy resins. Thepowder coating compositions are intended for application onheat-sensitive substrates producing finishes characterised by highhardness and a controllable gloss. Carboxyl functional polyestersoptionally can be added to the formulation as a flexibilising agent inamounts up to 50% yet nowhere are specified or illustrated.

EP 504,732 claims for powder coating compositions comprising acarboxylic acid group containing compound and/or resin, an epoxy groupcontaining compound and/or resin as well as a curing catalyst for lowtemperature curing applications. The carboxylic acid group containingcompound is a carboxylic acid group containing polyester or a carboxylicacid group containing acrylic copolymer. High gloss coatings with goodsolvent resistance are obtained after a 15 minute baking time at 160° C.

U.S. Pat. No. 6,294,610 claims for a binder composition for powdercoatings, comprising an epoxy resin, a carboxylic acid functionalpolymer and a particular catalyst. The carboxylic acid functionalpolymer can be a carboxylic acid functional polyester or a carboxylicacid group containing acrylic copolymer. When low temperature cureapplications are considered, the epoxy resin having an epoxy equivalentweight between 200 and 1000 preferably is an acrylic copolymer with aweight average molecular weight between 200 and 2000. The plate meltflow and gel times at 150° C. are compared for powders containing thecatalyst according to the invention, with those obtained from powdersconventionally catalysed. Powders are cured at temperatures ranging from150 to 175° C. for 5 minutes. Smooth low gloss finishes are obtained forpowders where the carboxylic acid containing compound comprises 8%weight of a crystalline polycarboxylic acid such as sebacic acid.

U.S. Pat. No. 6,407,181 claims for powder coating compositionscomprising a glycidyl group containing component and a carboxylic acidgroup containing component. The glycidyl group containing componentcomprises at least one glycidyl group containing acrylic copolymer withan epoxy equivalent weight of from 250 to 450 optionally in combinationwith a glycidyl group containing acrylic copolymer with an epoxyequivalent weight of from 500 to 800 and/or a crystalline aromaticepoxy. The carboxylic acid group containing component is a carboxylicacid group containing polyester with an acid number of from 30 to 60 mgKOH/g, optionally in combination with a crystalline polycarboxylic acidor anhydride and/or a carboxylic acid group containing acrylic copolymerwith an acid number of from 100 to 400 mg KOH/g. The powders areintended for smooth weatherable, reduced gloss coatings onheat-sensitive substrates. From all the examples as reproduced in table1 it appears that powder coating compositions comprising a glycidylgroup containing acrylic copolymer, an acid group containing polyester,and optionally a carboxylic acid group containing acrylic copolymer,upon curing at an oven set temperature between 350 to 425° C. for 5minutes, all present finishes with reduced gloss and a moderate to heavyorange peel.

JP 57-205458 claims a powder paint which comprises as a binder aco-reactable mixture of 60 to 96% weight of a carboxylic acid groupcontaining polyester with an acid number of from 20 to 200 mg KOH/g, 5to 40% weight of a glycidyl group containing acrylic copolymer with anumber average molecular weight of from 300 to 5000 and 1 to 20% weightof a carboxylic acid group containing acrylic copolymer having an acidnumber of from 10 to 200 mg KOH/g and a number average molecular weightof from 300 to 10000. The powder compositions which are free ofcatalysing compound for the reaction “carboxylic acid-epoxy”, areintended for smooth high gloss finishes which are obtained afterconventional curing cycles such as e.g. 20 minutes at 180° C.

All these powder coating compositions, as cited above, either aredeveloped for conventional curing schedules or, at low curingtemperatures, present drawbacks or limitations when a combination ofperformances such as a smooth aspect along with a good surface hardnessand weatherability are desired.

It now has been surprisingly found that powder coating compositionsderived from a binder comprising a particular correctable mixture of acarboxylic acid group containing polyester, a carboxylic acid groupcontaining acrylic copolymer and a glycidyl group containing acryliccopolymer, along with an appropriate amount of catalysing compoundallows, upon application and curing at temperatures of from 80 to 150°centigrade, for very smooth, reduced gloss finishes, proving goodsolvent resistance, hardness and weatherability, provided that at leastone of the glycidyl group containing acrylic copolymer, the carboxylicacid group containing acrylic copolymer and the carboxylic acid groupcontaining polyester is a low glass transition temperature polymer.

The present invention therefore relates to a thermosetting powdercoating composition comprising a co-reactable blend of

-   -   (i) 5 to 50 weight percent of at least one of glycidyl group        containing acrylic copolymer chosen between glycidyl group        containing acrylic copolymers (A) having a glass transition        temperature in the range of from +45 to +100° C. and a number        average molecular weight in the range of from 2000 to 5000,        glycidyl group containing acrylic copolymers (A′) having a glass        transition temperature in the range of from −50 to +40° C., and        their mixtures;    -   (ii) 5 to 90 weight percent of at least one carboxylic acid        group containing polyester chosen between carboxylic acid group        containing polyesters (B) having an acid number in the range of        from 15 to 100 mg KOH/g and a glass transition temperature in        the range of from +45 to +100° C., carboxylic acid group        containing polyesters (B′) having an acid number in the range of        from 15 to 100 mg KOH/g and a glass transition temperature of        from −50 to +40° C., and their mixtures;    -   (iii) 5 to 50 weight percent of at least one carboxylic acid        group containing acrylic copolymer chosen between carboxylic        acid group containing acrylic copolymers (C) having a glass        transition temperature in the range of from +45 to +100° C., an        acid number of from 10 to 90 mg KOH/g and a number average        molecular weight in the range of from 2000 to 5000, carboxylic        acid group containing acrylic copolymers (C′) having a glass        transition temperature in the range of from −50 to +40° C., an        acid number of from 10 to 90 mg KOH/g, and their mixtures; the        weight percentages being calculated on the whole of the        components (A), (A′), (B), (B′), (C) and (C′); and    -   (iv) a thermosetting catalyst (D)        provided that at least one of the low glass transition        temperature polymers (A′), (B′) and (C′) is present in the        composition.

By low or reduced gloss, it is intended that the gloss measured at anangle of 60° according to ASTM D 523, is inferior to 50%.

In the present invention the glass transition temperature is thismeasured by Differential Scanning Calorimetry according to ASTM D3418with a heating gradient of 20° C. per minute.

In the present invention, the number average molecular weight ismeasured by gel permeation chromatography (GPC).

The glycidyl group containing acrylic copolymer (A′) having a glasstransition temperature in the range of from −50 to +40° C. used in thecomposition according to the present invention preferably has a numberaverage molecular weight in the range of from 10000 to 20000.

The carboxylic acid group containing acrylic copolymer (C′) having aglass transition temperature in the range of from −50 to +40° C., anacid number of from 10 to 90 mg KOH/g preferably has a number averagemolecular weight in the range of from 10000 to 20000.

The glycidyl group containing acrylic copolymers (A) and (A′) used inthe present invention preferably have an epoxy equivalent weight of 1.0to 10.0 and more preferably 1.5 to 5.0 milli-equivalents of epoxy/gramof polymer.

The glycidyl group containing acrylic copolymers (A) and (A′) used inthe composition according to the present invention are preferablyobtained from 1 to 95 mole % of at least one glycidyl group containing(meth)acrylic monomer, preferably selected from glycidyl acrylate,glycidyl methacrylate, methyl glycidyl methacrylate, methyl glycidylacrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate, 1,2-ethyleneglycolglycidyl-ether(meth)acrylate,1,3-propyleneglycolglycidylether(meth)acrylate,1,4-butyleneglycolether(meth)acrylate,1,6-hexanediolether(meth)acrylate,1,3-(2-ethyl-2-butyl)-propanediolglycidylether(meth)acrylate and acrylicglycidyl ether.

The other monomers copolymerisable with the glycidyl group containingmonomer are used in mole percentages ranging from 5 to 99 and arepreferably selected from methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate,tert.butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,stearyl(meth)acrylate, tridecyl(meth)acrylate, cyclohexyl(meth)acrylate,n-hexyl(meth)acrylate, benzyl(meth)acrylate, phenyl(meth)acrylate,isobornyl(meth)acrylate, nonyl(meth)acrylate,hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate,hydroxybutyl(meth)acrylate, 1,4-butandiol mono(meth)acrylate, the estersof methacrylic acid, maleic acid, maleic anhydride, itaconic acid,dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate,styrene, α-methylstyrene, vinyl-toluene, (meth)acrylonitrile,vinylacetate, vinylpropionate, acrylamide, methacrylamide,methylol(meth)acrylamide, vinylchloride, ethylene, propylene, C4-20olefins and α-olefins. They can be used by themselves or in combinationof two or more.

The carboxylic acid group containing acrylic copolymers (C) and (C′) ofthe present invention have an acid number of from 10 to 90 mg KOH/g andpreferably of from 25 to 70 mg KOH/g.

The carboxylic acid group containing copolymers (C) and (C′) arepreferably obtained from 1 to 95 mole % of at least one carboxylic acidgroup containing monomer selected from acrylic acid, methacrylic acid,crotonic acid, itaconic acid, fumaric acid, maleic acid, citraconicacid, the monoalkylesters of unsaturated dicarboxylic acids. They can beused by themselves or in combination of two or more.

The other monomers copolymerisable with the carboxylic acid groupcontaining monomer are used in mole percentages ranging from 5 to 99 andare preferably selected from methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate,tert.butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,stearyl(meth)acrylate, tridecyl(meth)acrylate, cyclohexyl(meth)acrylate,n-hexyl(meth)acrylate, benzyl(meth)acrylate, phenyl(meth)acrylate,isobornyl(meth)acrylate, nonyl(meth)acrylate,hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate,hydroxybutyl(meth)acrylate, 1,4-butandiolmono(meth)acrylate, the estersof methacrylic acid, maleic acid, maleic anhydride, itaconic acid,dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate,styrene, α-methylstyrene, vinyltoluene, (meth)acrylonitrile,vinylacetate, vinylpropionate, acrylamide, methacrylamide,methylol(meth)acrylamide, vinylchloride, ethylene, propylene, C4-20olefins and α-olefins. They can be used by themselves or in combinationof two or more.

According to one embodiment of the present invention, the glycidyl groupcontaining acrylic copolymer (A) or the carboxylic acid group containingacrylic copolymer (C) can be used either alone.

According to another embodiment of the present invention, a blend of ahigh glass transition copolymer (A), respectively (C), and a low glasstransition acrylic copolymer (A′), respectively (C′), is used. When usedas a blend, the glycidyl group containing acrylic copolymer or thecarboxylic acid group containing acrylic copolymer, or both, arepreferably composed of:

-   -   −50 to 95 parts by weight of an acrylic copolymer (A),        respectively (C), having a glass transition temperature in the        range of from +45 to +100° C., and    -   5 to 50 parts by weight of an acrylic copolymer (A′),        respectively (C′), having a glass transition temperature in the        range of from −50 to +40° C.

As it is well known for those skilled in the art, a high Tg isobtainable depending on the proper choice of monomers. For example, mostof the methacrylates give copolymers with high Tg, while most of theacrylates give copolymers of low Tg. Mixtures of both types give anydesirable Tg.

The glycidyl group containing acrylic copolymer as well as thecarboxylic acid group containing copolymer is generally prepared byconventional polymerisation techniques, either in mass, in emulsion, orin the solution of an organic solvent. The nature of the solvent is verylittle of importance, provided that it is inert and that it readilydissolves the monomers and the synthesised copolymer. Suitable solventsinclude toluene, ethyl acetate, butyl acetate, xylene, etc. The monomersare usually copolymerised in the presence of a free radicalpolymerisation initiator (benzoyl peroxide, dibutyl peroxide,azo-bis-isobutyronitrile, and the like) in an amount representing 0.1 to4.0% by weight of the monomers.

To achieve a good control of the molecular weight and its distribution,a chain transfer agent, preferably of the mercaptan type, such asn-dodecylmercaptan, t-dodecanethiol, iso-octylmercaptan, or of thecarbon halide type, such as carbon tetrabromide, bromotrichloromethane,etc., can also added in the course of the reaction. The chain transferagent is usually used in amounts of up to 10% by weight of the monomersused in the copolymerisation.

A cylindrical, double walled reactor equipped with a stirrer, acondenser, an inert gas (nitrogen, for example) inlet and outlet, andmetering pump feeding systems is generally used to prepare the glycidylgroup containing acrylic copolymer. Polymerisation is carried out underconventional conditions. Thus, when polymerisation is carried out insolution, for example, an organic solvent is first introduced into thereactor and heated to the refluxing temperature under an inert gasatmosphere (nitrogen, carbon dioxide, and the like) and a homogeneousmixture of the required monomers, the free radical polymerisationinitiator and the chain transfer agent, when needed, is then added tothe solvent gradually over several hours. The reaction mixture is thenmaintained at the indicated temperature for certain hours, whilestirring. The solvent is then removed from the copolymer obtained invacuo.

The carboxyl functional polyesters of the present invention have an acidnumber from 15 to 100 mg KOH/g and preferably from 30 to 70 mg KOH/g.

According to one embodiment of the present invention, the carboxylfunctional polyester (B) is used alone. According to another embodimentof the invention, the carboxyl functional polyester (B) is used incombination with a low Tg polyester (B′). The carboxyl functionalpolyester (B) is preferably an amorphous polyester. The carboxylfunctional polyester (B′) is preferably a semi-crystalline polyester.

When a blend is used, the weight ratio between the amorphous polyester(B) and the semi-crystalline polyester (B′) preferably ranges from 95:5to 50:50.

The carboxyl functional polyesters (B) preferably used in thecomposition according to the invention have:

-   -   an number averaged molecular weight ranging from 1100 to 15000        and more preferably from 1600 to 8500,    -   an ICI cone and plate viscosity according to ASTM D4287-88,        measured at 200° C. ranging from 5 to 15000 mPa·s.

The carboxyl functional polyester (B) is usually obtained from an acidconstituent and a polyol constituent. The acid constituent is preferablycomposed of from 50 to 100 molar percent of terephthalic or isophthalicacid or their mixtures and from 0 to 50 molar percent of anotherpolyacid constituent selected from one or more aliphatic, cycloaliphaticor aromatic polyacids, such as: fumaric acid, maleic acid, phthalicanhydride, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylicacid, 1,2-cyclohexanedicarboxylic acid, succinic acid, adipic acid,glutaric acid, pimelic acid, suberic acid, azealic acid, sebacic acid,1,12-dodecanedioic acid, trimellitic acid or pyromellitic acid, etc., orthe corresponding anhydrides.

The polyol constituent of the polyester (B), used in the compositionaccording to the present invention, is preferably composed of from 40 to100 molar percent of neopentyl glycol and from 0 to 60 molar percent ofanother polyol constituent selected from one or more aliphatic orcycloaliphatic polyols such as: ethylene glycol, propylene glycol,1,4-butanediol, 1,6-hexanediol, 1,4cyclohexanediol,1,4-cyclohexanedimethanol, 2-methyl-1,3-propanediol,2-butyl-2-ethyl-1,3-propanediol, hydrogenated Bisphenol A,hydroxypivalate of neopentyl glycol, trimethylolpropane,ditrimethylolpropane, pentaerythritol, etc.

The carboxyl functional polyesters (B′) used in the compositionaccording to the present invention have a carboxyl number from 15 to 100mg KOH/g and preferably from 30 to 70 mg KOH/g

The carboxyl functional polyesters (B′) are further preferablycharacterised by:

-   -   a number averaged molecular weight ranging from 1100 to 17000        and more preferably from 1400 to 11200    -   a fusion zone from 50 to 150° C., measured by Differential        Scanning Calorimetry (DSC) according to ASTM D3418 with a        heating gradient of 20° C. per minute    -   a glass transition temperature (Tg) of below 40° C.    -   a degree of crystallinity, measured by Differential Scanning        Calorimetry (DSC) according to ASTM D3415 of at least 5 J/g and        more preferably at least 10 J/g    -   an ICI (cone/plate) viscosity according to ASTM D4287-88,        measured at 100° C. of at least 100 mPa·s.

The polyester (B′) used in the composition according to the presentinvention, is usually obtained from an acid constituent and a polyolconstituent. The acid constituent is preferably composed of from 70 to100 molar percent of terephthalic acid, 1,4-cyclo-hexanedicarboxylicacid and/or a linear chain dicarboxylic acid containing from 4 to 16carbon atoms such as succinic acid, adipic acid, glutaric acid, pimelicacid, suberic acid, azelaic acid, sebacic acid, 1,10-decanedioic acid,1,11-undecanedioic acid, 1,12-dodecanedioic acid, 1,13-triadecanedioicacid, 1,14-tetradecanedioic acid, 1,15-pentadecanedioic acid,1,16-hexadecanedioic acid, etc. used in a mixture or alone, and from 30to 0 molar percent of at least one other aliphatic, cycloaliphatic oraromatic polyacid such as: fumaric acid, maleic anhydride, phthalicanhydride, isophthalic acid, 1,3-cyclohexanedicarboxylic acid,1,2-cyclohexanedicarboxylic acid, etc.

The polyol constituent of the polyester (B′) is preferably composed offrom 70 to 100 molar percent of a cycloaliphatic and/or linear-chainaliphatic diol containing 2 to 16 carbon atoms such as1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated BisphenolA, 2,2,4,4-tetramethyl-1,3-cyclobutanol or4,8-bis(hydroxymethyl)tri-cyclo[5.2.1.0]decane, ethylene glycol,1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol,14-tetradecanediol, 1,16-hexadecanediol, etc. used in a mixture ofalone, and from 30 to 0 molar percent of at least one other aliphaticpolyol such as: propylene glycol, neopentyl glycol,2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol,hydroxypivalate of neopentyl glycol, etc.

The carboxylic acid group containing polyester (B) and the carboxylicacid group containing polyester (B′) used in the composition accordingto the present invention, can be prepared using conventionalesterification techniques well known in the art. The polyesters areusually prepared according to a procedure consisting of one or morereaction steps.

The carboxylic acid group containing polyesters also can be obtainedfrom the ring opening reaction of an anhydride of a polybasic organiccarboxylic acid on the hydroxyl group of the hydroxyl group containingpolyester at a temperature of from 120 to 200° C. until the desired acidand/or hydroxyl numbers are obtained.

The thermosetting catalyst (D) used in the composition according to theinvention is generally added in order to accelerate cross-linkingreactions of the thermosetting powder composition during curing.Preferred examples of such catalysts include amines (e.g.2-phenylimidazoline), phosphines (e.g. triphenylphosphine), ammoniumsalts (e.g. tetrabutylammonium bromide or tetrapropylammonium chloride),phosphonium salts (e.g. ethyltriphenylphosphonium bromide ortetrapropylphosphonium chloride) or acid blocked catalysts such as forexample acid blocked amine or phosphine catalysts. These catalysts arepreferably used in an amount of from 0.1 to 5% with respect to the totalweight of (A), (A′), (B), (B′), (C) and (C′).

According to a preferred embodiment of the invention, the compositioncomprises a glycidyl group containing acrylic copolymer (A) having aglass transition temperature in the range of from +45 to +100° C., of aglycidyl group containing acrylic copolymer (A′) having a glasstransition temperature in the range of from −50 to +40° C., a carboxylicacid group containing amorphous polyester (B) having a glass transitiontemperature in the range of from +45 to +100° C., of a carboxylic acidgroup containing acrylic copolymer (C) having a glass transitiontemperature in the range of from +45 to +100° C., and a thermosettingcatalyst (D) selected from the phosphines, amines, phosphonium salt,ammonium salt, acid blocked amine or acid blocked phosphine typecompounds.

According to another preferred embodiment of the invention, thecomposition comprises a glycidyl group containing acrylic copolymer (A)having a glass transition temperature in the range of from +45 to +100°C., a carboxylic acid group containing amorphous polyester (B) having anacid number in the range of from 15 to 100 mg KOH/g and a glasstransition temperature in the range of from +45 to +100° C., acarboxylic acid group containing semi-crystalline polyester (B′) havingan acid number in the range of from 15 to 100 mg KOH/g and a glasstransition temperature in the range of from −50 to +40° C., a carboxylicacid group containing acrylic copolymer (C) having a glass transitiontemperature in the range of from +45 to +100° C., an acid number of from10 to 90 mg KOH/g and a thermosetting catalyst (D) selected from thephosphines, amines, phosphonium salt, ammonium salt, acid blocked amineor acid blocked phosphine type compounds.

According to yet another preferred embodiment of the present invention,the composition comprises a glycidyl group containing acrylic copolymer(A) having a glass transition temperature in the range of from +45 to+100° C., a carboxylic acid group containing amorphous polyester (B)having an acid number in the range of from 15 to 100 mg KOH/g and aglass transition temperature in the range of from +45 to +100° C., acarboxylic acid group containing acrylic copolymer (C) having a glasstransition temperature in the range of from +45 to +100° C., to 5000, acarboxylic acid group containing acrylic copolymer (C′) having a glasstransition temperature in the range of from −50 to +40° C., and athermosetting catalyst (D) selected from the phosphines, amines,phosphonium salt, ammonium salt, acid blocked amine or acid blockedphosphine type compounds.

According to another preferred embodiment of the invention, thecomposition comprises a glycidyl group containing acrylic copolymer (A)having a glass transition temperature in the range of from +45 to +100°C., a glycidyl group containing acrylic copolymer (A′) having a glasstransition temperature in the range of from −50 to +40° C., of acarboxylic acid group containing amorphous polyester (B) having an acidnumber in the range of from 15 to 100 mg KOH/g and a glass transitiontemperature in the range of from +45 to +100° C., a carboxylic acidgroup containing acrylic copolymer (C) having a glass transitiontemperature in the range of from +45 to +100° C., a carboxylic acidgroup containing acrylic copolymer (C′) having a glass transitiontemperature in the range of from −50 to +40° C. and a thermosettingcatalyst (D) selected from the phosphines, amines, phosphonium salt,ammonium salt, acid blocked amine or acid blocked phosphine typecompound.

According to yet another preferred embodiment according to theinvention, the composition comprises a glycidyl group containing acryliccopolymer (A) having a glass transition temperature in the range of from+45 to +100° C., of a glycidyl group containing acrylic copolymer (A′)having a glass transition temperature in the range of from −50 to +40°C., a carboxylic acid group containing amorphous polyester (B) having anacid number in the range of from 15 to 100 mg KOH/g and a glasstransition temperature in the range of from +45 to +100° C., acarboxylic acid group containing semi-crystalline polyester (B′) havingan acid number in the range of from 15 to 100 mg KOH/g and a glasstransition temperature in the range of from −50 to +40° C., a carboxylicacid group containing acrylic copolymer (C) having a glass transitiontemperature in the range of from +45 to +100° C., and a thermosettingcatalyst (D) selected from the phosphines, amines, phosphonium salt,ammonium salt, acid blocked amine or acid blocked phosphine typecompounds.

According to yet another preferred embodiment of the invention, thecomposition comprises a glycidyl group containing acrylic copolymer (A)having a glass transition temperature in the range of from +45 to +100°C., a carboxylic acid group containing amorphous polyester (B) having anacid number in the range of from 15 to 100 mg KOH/g and a glasstransition temperature in the range of from +45 to +100° C., acarboxylic acid group containing semi-crystalline polyester (B′) havingan acid number in the range of from 15 to 100 mg KOH/g and a glasstransition temperature in the range of from −50 to +40° C., a carboxylicacid group containing acrylic copolymer (C) having a glass transitiontemperature in the range of from +45 to +100° C., a carboxylic acidgroup containing acrylic copolymer (C′) having a glass transitiontemperature in the range of from −50 to +40° C., an acid number of from10 to 90 mg KOH/g and a number average molecular weight in the range offrom 10000 to 20000, and a thermosetting catalyst (1) selected from thephosphines, amines, phosphonium salt, ammonium salt, acid blocked amineor acid blocked phosphine type compound.

Finally, according to another preferred embodiment of the invention, thecomposition comprises a glycidyl group containing acrylic copolymer (A)having a glass transition temperature in the range of from +45 to +100°C., a glycidyl group containing acrylic copolymer (A′) having a glasstransition temperature in the range of from −50 to +40° C., a carboxylicacid group containing amorphous polyester (B) having an acid number inthe range of from 15 to 100 mg KOH/g and a glass transition temperaturein the range of from +45 to +100° C., a carboxylic acid group containingsemi-crystalline polyester (B′) having an acid number in the range offrom 15 to 100 mg KOH/g and a glass transition temperature in the rangeof from −50 to +40° C., a carboxylic acid group containing acryliccopolymer (C) having a glass transition temperature in the range of from+45 to +100° C., a carboxylic acid group containing acrylic copolymer(C′) having a glass transition temperature in the range of from −50 to+40° C., and a thermosetting catalyst (D) selected from the phosphines,amines, phosphonium salt, ammonium salt, acid blocked amine or acidblocked phosphine type compound.

The binder system of the thermosetting composition of the invention ispreferably composed in such a way that for each equivalent of carboxylgroup present in the carboxylic acid group containing polyester ((B)and/or (B′)) and the carboxylic acid group containing acrylic copolymer((C) and/or (C′)), there is between 0.3 and 2.0 and more preferablybetween 0.6 and 1.7 equivalents of epoxy groups from the glycidyl groupcontaining acrylic copolymer ((A) and/or (A′)).

In addition to the essential components described above, compositionswithin the scope of the present invention can also include flow controlagents such as Resiflow P-675 (Estron), Modaflow (Monsanto), Acronal 4F(BASF), etc., and degassing agents such as Benzoin (BASF) etc. To theformulation UV-light absorbers such as Tinuvin 900 (Ciba), hinderedamine light stabilisers represented by Tinuvin 144 (Ciba), otherstabilising agents such as Tinuvin 312 and 1130 (Ciba), antioxidantssuch as Irganox 1010 (Ciba) and stabilisers of phosphonite or phosphitetypes can also be added.

Both pigmented and clear lacquers can be prepared. A variety of dyes andpigments can be utilised in the composition of this invention. Examplesof useful pigments and dyes are: metallic oxides such as titaniumdioxide, iron oxide, zinc oxide and the like, metal hydroxides, metalpowders, sulphides, sulphates, carbonates, silicates such as ammoniumsilicate, carbon black, talc, china clay, barytes, iron blues,leadblues, organic reds, organic maroons and the like.

The components of the composition according to the invention may bemixed by dry blending in a mixer or blender (e.g. drum mixer). Thepremix is then homogenised at temperatures ranging from 50 to 120° C. ina single screw extruder such as the BUSS-Ko-Kneter or a twin screwextruder such as the PRISM or APV. The extrudate, when cooled down, isground to a powder with a particle size ranging from 10 to 150 μm. Thepowdered composition may be deposited on the substrate by use of apowder gun such as an electrostatic CORONA gun or TRIBO gun. On theother hand, well known methods of powder deposition such as thefluidised bed technique can also be used. After deposition the powder isusually heated to a temperature between 80 and 150° C., causing theparticles to flow and fuse together to form a smooth, uniform,continuous, uncratered coating on the substrate surface.

The present invention further relates to the use of the thermosettingpowder coating composition according to the invention to coat metallicand non-metallic surfaces, especially heat sensitive substrates such aspaper, card board, wood, fibre board, textiles, polycarbonates, poly(meth)acrylates, polyolefins, polystyrenes, polyvinylchlorides,polyesters, polyurethanes, polyamides, copolymers of acrylonitrilebutadiene styrene and cellulose acetate butyrate; and to thepartially-or entirely coated substrates thereby obtained.

The following examples are submitted for a better understanding of theinvention without being restricted thereto.

EXAMPLE 1 & 2 Synthesis of a High Tg-Low Mn and of a Low Tg-High MnGlycidyl Group Containing Acrylic Copolymer

Step 1: Synthesis of the Low Tg Resin with High Molecular Weight (A′)

261.38 parts of n-butylacetate are brought in a double walled flask of 5l equipped with a stirrer, a water cooled condenser and an inlet fornitrogen and a thermoprobe attached to a thermoregulator.

The flask content is heated and stirred continuously while nitrogen ispurged through the solvent. At a temperature of 92±1° C. a mixture of65.34 parts of n-butylacetate with 0.82 parts of 2,2′-azobis (2-methylbutanenitrile) is fed in the flask during 215 minutes with a peristalticpump. 5 minutes after the start of this feed, a second one is startedwith another pump, which is a mixture of M1

This feed takes 180 minutes.

After 315 minutes of total synthesis time, the synthesis temperature iskept constant at 92±1° C. (mass temperature measuring) and step 2 isstarted with.

Step 2: Synthesis of the High Tg Resin with Low Molecular Weight (A) inthe Prepolymer Created in Step 1

The flask content described in step 1 is continuously being purged withnitrogen. At the same temperature of 92±1° C. a mixture of 81.68 partsof n-butylacetate with 5.17 parts of 2,2′-azobis (2-methylbutanenitrile) is fed in the flask during 215 minutes with a peristalticpump. 5 minutes after the start of this feed, a second one is startedwith another pump, which is a mixture of M2

This feed takes 180 minutes.

After 315 minutes of total synthesis time for step 2, the flask contentis transversed gradually in a rotary evaporator during a period of 120minutes. Before the drying cycle the ambient pressure in the rotaryevaporator is reduced to 10 hPa. The temperature of the oil, which heatsthe evaporator flask content, is kept at 180° C. during the entireevaporation cycle. After 180 minutes of evaporation, the acrylic resinwith absence of solvent is isolated and cooled down to room temperature.A sample is taken for residual solvent content analysis by gaschromatography. The residual solvent content should be lower than 0.3%weight. Example 1 Example 2 M1 GMA 91.48 68.61 BuA 71.88 79.67 BuMA 15.7Tg, ° C. −22 −20 Mn 11240 11000 M2 GMA 228.7 171.53 MMA 39.12 91.03 BuMA44.93 Styrene 140.57 100.92 Tg, ° C. 57 54 Mn 4450 4500 Brookfieldviscosity at 200° C., 2000 2500 mPa.s EEW, g/equiv. 257 390

The obtained mixtures in both examples 1 and 2 are thus blends of 28.6%by weight of a low Tg glycidyl group containing acrylic copolymer (A′)with 71.4% by weight of a high Tg glycidyl group containing acryliccopolymer (A) In this table the following abbreviations are used:

-   -   GMA glycidyl methacrylate    -   BuA butyl acrylate    -   BuMA butyl methacrylate    -   MMA methyl methacrylate    -   Tg glass transition temperature    -   Mn number average molecular weight    -   EEW epoxy equivalent weight

EXAMPLE 3 Synthesis of a High Tg-Low Mn Glycidyl Group ContainingAcrylic (A)

390.88 parts of n-butylacetate are brought in a double walled flask of 5l equipped with a stirrer, a water cooled condenser and an inlet fornitrogen and a thermoprobe attached to a thermoregulator.

The flask content is heated and stirred continuously while nitrogen ispurged through the solvent. At a temperature of 92±1° C. a mixture of97.72 parts of n-butylacetate with 6.18 parts of 2,2′-azobis (2-methylbutanenitrile) is fed in the flask during 215 minutes with a peristalticpump. 5 minutes after the start of this feed, a second one is startedwith another pump and is mixture 273.62 parts of glycidyl methacrylate,46.81 parts of methyl methacrylate and 168.18 parts of styrene

This feed takes 180 minutes.

After 315 minutes of total synthesis time, the flask content istransversed gradually in a rotary evaporator during a period of 120minutes. Before the drying cycle the ambient pressure in the rotaryevaporator is reduced to 10 hPa. The temperature of the oil, which heatsthe evaporator flask content, is kept at 180° C. during the entireevaporation cycle. After 180 minutes of evaporation, the acrylic resinwith absence of solvent is isolated and cooled down to room temperature.A sample is taken for residual solvent content analysis by gaschromatography. The residual solvent content should be lower than 0.3%weight.

The glycidyl group containing acrylic copolymer, thus obtained, ischaracterised by an epoxy equivalent weight (EEW) of 260 g/equiv., anumber average molecular weight of 4300, a glass transition temperatureof 55° C. and a Brookfield cone/plate viscosity of 3600 mPa·s measuredat 200° C.

EXAMPLE 4 & 5 Synthesis of a High Tg-Low Mn and of a Low Tg-High MnCarboxylic Acid Group Containing Acrylic Copolymer

Step 1: Synthesis of the Low Tg Resin with High Molecular Weight (C′)

261.1 parts of n-butylacetate are brought in a double walled flask of 5l equipped with a stirrer, a water cooled condenser and an inlet fornitrogen and a thermoprobe attached to a thermoregulator.

The flask content is heated and stirred continuously while nitrogen ispurged through the solvent. At a temperature of 125±1° C. a mixture of65.0 parts of n-butylacetate with 0.81 parts of t-butyl peroxybenzoateis fed in the flask during 215 minutes with a peristaltic pump. 5minutes after the start of this feed, a second one is started withanother pump, which is a mixture of M1

This feed takes 180 minutes.

After 315 minutes of total synthesis time, the synthesis temperature iskept constant at 125±1° C. (mass temperature measuring) and step 2 isstarted with

Step 2: Synthesis of the High Tg Resin with Low Molecular Weight (C) inthe Prepolymer Created in Step 1.

The flask content described in step 1 is continuously being purged withnitrogen. At the same temperature of 125±1° C. a mixture of 80.57 partsof n-butylacetate with 12.23 parts of t-butyl peroxybenzoate is fed inthe flask during 215 minutes with a peristaltic pump. 5 minutes afterthe start of this feed, a second one is started with another pump, whichis a mixture of M2

This feed takes 180 minutes.

After 315 minutes of total synthesis time for step 2, the flask contentis transversed gradually in a rotary evaporator during a period of 120minutes. Before the drying cycle the ambient pressure in the rotaryevaporator is reduced to 10 hPa. The temperature of the oil, which heatsthe evaporator flask content, is kept at 180° C. during the entireevaporation cycle. After 180 minutes of evaporation, the acrylic resinwith absence of solvent is isolated and cooled down to room temperature.A sample is taken for residual solvent content analysis by gaschromatography. The residual solvent content should be lower than 0.3%weight. Example 4 Example 5 M1 MA (methacrylic acid) 8.32 13.75 MMA10.93 5.47 BuA 111.26 111.03 Styrene 32.63 32.56 Tg, ° C. −12 −10 Mn12560 11800 M2 MA 20.80 34.37 MMA 142.33 128.44 BuMA 163.13 162.80Styrene 81.57 81.40 Tg, ° C. 49 52 Mn 6070 5900 Brookfield viscosity at200° C., 2000 2500 mPa.s Acid number, mg KOH/g 30.6 50.0

The obtained mixtures in both examples 4 and 5 are thus blends of 28.6%by weight of a low Tg carboxyl group containing acrylic copolymer (C′)with 71.4% by weight of a high Tg carboxyl group containing acryliccopolymer (C).

EXAMPLE 6 & 7 Synthesis of a High Tg-Low Mn Carboxylic Acid GroupContaining Acrylic Copolymer (C). EXAMPLE 6

390.16 parts of n-butylacetate are brought in a double walled flask of 5l equipped with a stirrer, a water cooled condenser and an inlet fornitrogen and a thermoprobe attached to a thermoregulator.

The flask content is heated and stirred continuously while nitrogen ispurged through the solvent. At a temperature of 125±1° C. a mixture of97.54 parts of n-butylacetate with 14.63 parts of t-butyl peroxybenzoateis fed in the flask during 215 minutes with a peristaltic pump. 5minutes after the start of this feed, a second one is started withanother pump, which is a mixture of 25.09 parts of methacrylic acid,97.54 parts of styrene, 195.08 parts of butyl methacrylate and 170.21parts of methyl methacrylate.

This feed takes 180 minutes. The carboxylic acid group containingacrylic copolymer is characterised by an acid number of 30.2 mg KOH/g, anumber average molecular weight of 4800, a Brookfield cone/plateviscosity, measured at 200° C. of 3000 mPa·s and a glass transitiontemperature of 57° C.

EXAMPLE 7 (COMPARATIVE EXAMPLE)

386.54 parts of n-butanol are brought in a double walled flask of 5 lequipped with a stirrer, a water cooled condenser and an inlet fornitrogen and a thermoprobe attached to a thermoregulator.

The flask content is heated and stirred continuously while nitrogen ispurged through the solvent. At a temperature of 118±1° C. a mixture of96.64 parts of n-butanol with 14.50 parts of t-butyl peroxybenzoate isfed in the flask during 215 minutes with a peristaltic pump. 5 minutesafter the start of this feed, a second one is started with another pumpwhich is a mixture of 87.89 parts of methacrylic acid, 96.64 parts ofstyrene, 193.27 parts of butyl methacrylate and 105.21 parts of methylmethacrylate

This feed takes 180 minutes. The carboxylic acid group containingacrylic copolymer is characterised by an acid number of 102 mg KOH/g, anumber average molecular weight of 5300, a Brookfield cone/plateviscosity, measured at 200° C. of 9300 mPa·s and a glass transitiontemperature of 63° C.

After 315 minutes of total synthesis time, the flask content for example6 & 7, respectively is transversed gradually in a rotary evaporatorduring a period of 120 minutes. Before the drying cycle the ambientpressure in the rotary evaporator is reduced to 10 hPa. The temperatureof the oil, which heats the evaporator flask content, is kept at 180° C.during the entire evaporation cycle. After 180 minutes of evaporation,the acrylic resin with absence of solvent is isolated and cooled down toroom temperature. A sample is taken for residual solvent contentanalysis by gas chromatography. The residual solvent content should belower than 0.3% weight.

EXAMPLE 8 Synthesis of a Carboxylic Acid Group Containing Polyester (B)

422.30 parts of neopentyl glycol is placed in a conventional four neckround bottom flask equipped with a stirrer, a distillation columnconnected to a water cooled condenser, an inlet for nitrogen and athermometer attached to a thermoregulator.

The flask contents are heated, while stirring under nitrogen, to atemperature of circa 140° C. at which point 573.15 parts of terephthalicacid, 30.17 parts of adipic acid and 1.25 parts of n-butyltintrioctoateare added. The reaction is continued at 240° C. under atmosphericpressure until about 95% of the theoretical amount of water is distilledand a transparent hydroxyl functionalised prepolymer with followingcharacteristics is obtained:AN=7.6 mg KOH/gOHN=56.6 mg KOH/g

To the first step prepolymer standing at 200° C., 110.14 parts ofisophthalic acid is added. Thereupon, the mixture is gradually heated to230° C. After a 2 hour period at 230° C. and when the reaction mixtureis transparent, 1.0 part of tributylphosphite and 1.0 part ofn-butyltintrioctoate are added and a vacuum of 50 mm Hg is graduallyapplied. After 3 hours at 230° C. and 50 mm Hg, followingcharacteristics are obtained:AN=35.5 mg KOH/gOHN=2.5 mg KOH/gBrookField^(200° C.) (Cone/Plate)=5000 mPa·s

The carboxyl functionalised polyester is cooled down to 180° C. and theresin is discharged.

EXAMPLE 9 Synthesis of a Carboxylic Acid Group Containing Polyester (B)

A mixture of 375.2 parts of neopentyl glycol and 1.9 parts of n-butyltintrioctoate is placed in a conventional four-neck round bottom flask asin example 8.

The flask contents are heated while stirring, under nitrogen to atemperature of circa 140° C. Thereupon 483.3 parts of terephthalic acidalong with 47.8 parts of adipic acid are added while stirring and themixture is gradually heated to a temperature of 230° C. Distillationstarts from about 185° C. After about 95% of the theoretical quantity ofwater is distilled and a transparent prepolymer is obtained, the mixtureis cooled down to 200° C.

The hydroxyl functionalised prepolymer thus obtained, is characterisedby:AN=8 mg KOH/gOHN=60 mg KOH/g

To the first step prepolymer standing at 200° C., 56.9 parts oftrimellitic anhydride and 36.7 parts of adipic acid are added. Thereuponthe mixture is gradually heated to 225° C. After a two-hour period at225° C. and when the reaction mixture is transparent, 0.8 parts oftributylphosphite are added and a vacuum of 50 mm Hg is graduallyapplied. After 3 hours at 225° C. and 50 mm Hg, followingcharacteristics are obtained:AN=48 mg KOH/gOHN=6 mg KOH/gBrookfield^(175° C.)=8700 mPa·s

EXAMPLE 10 Synthesis of a (cyclo)aliphatic Semi-Crystalline Polyester(B′)

A mixture of 532.1 parts of 1,4-cyclohexanedimethanol, 15.9 parts oftriethylolpropane, 591.3 parts of adipic acid and 2.5 parts ofn-butyltintrioctoate is placed in a reactor as for Example 8. The flaskcontents are heated, while stirring under nitrogen to a temperature ofcirca 140° C., at which point water is distilled from the reactor. Theheating is continued gradually to a temperature of 220° C. Whendistillation under atmospheric pressure stops, 1.0 part oftributylphosphite and 1.0 part of n-butyltintrioctoate are added and avacuum of 50 mm Hg is gradually applied.

After 5 hours at 220° C. and 50 mm Hg, the following characteristics areobtained: AN 22 mg KOH/g OHN  3 mg KOH/g Brookfield^(200°C.)(cone/plate)  6800 mPa.s Fusion zone 79-96° C.

EXAMPLE 11

The glycidyl group containing acrylic copolymers of example 1 to 3, thecarboxylic acid group containing acrylic copolymers of example 4 to 7,the polyesters of example 8 to 10 along with an imidazole type catalyst(Epicure P1) are then formulated to a powder accordingly to one of theformulations as mentioned below. Formulation A Formulation B White paintformulation Brown paint formulation Binder 69.06 Binder 78.33 Kronos2310 29.60 Bayferrox 130 4.44 Resiflow PV5 0.99 Bayferrox 3950 13.80Benzoin 0.35 Carbon Black FW2 1.09 Epicure P1 0.50 Resiflow PV5 0.99Benzoin 0.35 Epicure P1 0.50

The powders are prepared first by dry blending of the differentcomponents and then by homogenisation in the melt using a PRISM 16 mmL/D 15/1 twin screw extruder at an extrusion temperature of 85° C. Thehomogenised mix is then cooled and grinded in an Alpine. Subsequentlythe powder is sieved to obtain a particle size between 10 and 110 μm.The powder thus obtained is deposited on chromated (Cr⁶⁺) aluminiumH5005, DIN 50939 with a thickness of 1 mm, by electrostatic depositionusing the GEMA-Volstatic PCG 1 spray gun. At a film thickness between 50and 80 μm the panels are transferred to an air-ventilated oven, wherecuring proceeds for 10 minutes at a temperature of 140° C. and for 25minutes at 120° C. respectively. The paint characteristics for thefinished coatings are given in the table hereafter. FormulationFormulation Glycidyl Carboxyl Carboxyl Pencil Number Type AcrylicAcrylic Polyester Gloss Visual Hardness MEK-rubs Ex. 12 A Ex. 1: 12.0Ex. 4: 44.0 Ex. 8: 44.0 7/8 g/g 2H/2H >200/>200 Ex. 13 A Ex. 2: 25.4 Ex.5: 37.3 Ex. 9: 37.3 30/29 g/g 3H/3H >200/>200 Ex. 14 A Ex. 2: 20.0 Ex.5: 20.0 Ex. 8: 60.0 10/10 g/g 3H/3H >200/>200 Ex. 15 A Ex. 2: 20.0 Ex.5: 20.0 Ex. 8: 54.0 8/9 g/g H/H >200/>200 Ex. 10: 6.0 Ex. 16 B Ex. 2:20.0 Ex. 5: 20.0 Ex. 8: 54.0 10/10 g/g H/H >200/>200 Ex. 10: 6.0 Ex. 17A Ex. 1: 12.0 Ex. 6: 44.0 Ex. 8: 44.0 10/9  g/g 3H/3H >200/>200 Ex. 18 AEx. 3: 12.0 Ex. 4: 44.0 Ex. 8: 44.0 11/12 g/g 2H/3H >200/>200 Ex. 19 AEx. 3: 12.0 Ex. 6: 44.0 Ex. 8: 44.0 5/5 b-t/b-t 3H/3H >200/>200 Ex. 20 AEx. 1: 22.8 Ex. 7: 38.6 Ex. 8: 38.6 8/8 t-s/t-s 3H/3H >200/>200

In this table:

Column 1: indicates the identification number of the formulation

Column 2: indicates the type of formulation

-   -   A=white (RAL9010)    -   B=medium brown (RAL8014)

Column 3: indicates the type and quantity of the glycidyl groupcontaining acrylic copolymer (A), or (A) and (A′), used in the binder

Column 4: indicates the type and quantity of the carboxylic acid groupcontaining acrylic copolymer (C), or (C) and (C′), used in the binder

Column 5: indicates the type and quantity of the carboxylic acid groupcontaining polyester (B), or (B) and (B′), used in the binder

Column 6: indicates the 60° gloss, measured according to ASTM D523 (10′at 140° C./25′ at 120° C.)

Column 7: indicates the aspect of the coating (10′ at 140° C./25′ at120° C.)

-   -   G: very smooth    -   B: strong orange peel    -   T: textured    -   S: sandpaper-like

Column 8: indicates the pencil hardness according to the scratchHardness Tester according to Wolff-Wilborn. (10′ at 140° C./25′ at 120°C.)

Column 9: indicates the resistance to MEK, which corresponds to thenumber of twofold rubbing movements (to and fro) with a cotton padimpregnated with MEK which does not detrimentally affect the appearanceof the surface of the cured film. (10′ at 140° C/25′ at 120° C.)

As clearly appears from examples 12 to 18, smooth low gloss finishes canbe obtained from the powder coating compositions according to thepresent invention.

On the contrary, powder coating compositions comprising a carboxylicacid group containing polyester along with a high Tg-low Mn carboxylicacid group containing acrylic copolymer and a high Tg-low Mn glycidylgroup containing acrylic copolymer, upon application and curing, presentlow gloss coatings proving strong orange peel and/or atextured-sandpaper-like aspect.

Besides, the coatings according to the present invention all prove tosatisfy an excellent outdoor resistance, comparable to or better thanthe currently used nowadays commercial available powders.

Thus, upon submitting the coating obtained from the powder of Ex. 16 tothe Q-UV accelerated weathering test, 2200 hours of exposure are neededfor a reduction of the relative 60° gloss value (ASTM D523) to 50% ofthe initial value, meanwhile a ΔE*-valueΔE*=√{square root over ((L ₀ *−L*)²+(a ₀ *−a*)²+(b ₀ *−b*)²)}(according to “Compagnie Internationale d'Eclairage” L*a*b*-colourmeasurement method (CIE-L*a*b*)) of 4 is measured after 1500 hrs ofexposure.

Weathering measurements are conducted in a very severe environment, i.e.the Q-UV accelerated weathering tester (Q-Panel Co) according to ASTMG53-88 (standard practice for operating light and water exposureapparatus—fluorescent UV/condensation type—for exposure of non metallicmaterials).

For these measurements, coated panels are subjected to the intermittenteffects of condensation (4 hours at 50° C.) as well as the damagingeffects of sunlight simulated by fluorescent UV-A lamps (340 nm, I=0.77W/m²/nm) (8 hours at 60° C.).

1. Thermosetting powder coating composition comprising a co-reactableblend of (i) 5 to 50 weight percent of at least one of glycidyl groupcontaining acrylic copolymer chosen between glycidyl group containingacrylic copolymers (A) having a glass transition temperature in therange of from +45 to +100° C. and a number average molecular weight inthe range of from 2000 to 5000, glycidyl group containing acryliccopolymers (A′) having a glass transition temperature in the range offrom −50 to +40° C., and their mixtures; (ii) 5 to 90 weight percent ofat least one carboxylic acid group containing polyester chosen betweencarboxylic acid group containing polyesters (B) having an acid number inthe range of from 15 to 100 mg KOH/g and a glass transition temperaturein the range of from +45 to +100° C., carboxylic acid group containingpolyesters (B′) having an acid number in the range of from 15 to 100 mgKOH/g and a glass transition temperature of from −50 to +40° C., andtheir mixtures; (iii) 5 to 50 weight percent of at least one carboxylicacid group containing acrylic copolymer chosen between carboxylic acidgroup containing acrylic copolymers (C) having a glass transitiontemperature in the range of from +45 to +100° C., an acid number of from10 to 90 mg KOH/g and a number average molecular weight in the range offrom 2000 to 5000, carboxylic acid group containing acrylic copolymers(C′) having a glass transition temperature in the range of from −50 to+40° C., an acid number of from 10 to 90 mg KOH/g, and their mixtures;the weight percentages being calculated on the whole of the components(A), (A′), (B), (B′), (C) and (C′); and (iv) a thermosetting catalyst(D) provided that at least one of the low glass transition temperaturepolymers (A′), (B′) and (C′) is present in the composition. 2.Composition according to claim 1 wherein the glycidyl group containingacrylic copolymers (A) and (A′) have an epoxy equivalent weight of from1.0 to 10.0 and preferably 1.5 to 5.0 milli-equivalents of epoxy pergram of acrylic copolymer.
 3. Composition according to claim 1, whereinthe glycidyl group containing acrylic copolymers (A) and (A′) areprepared from 1 to 95% mole of at least one glycidyl group containing(meth)acrylic monomer selected from glycidyl acrylate, glycidylmethacrylate, methyl glycidyl methacrylate, methyl glycidyl acrylate,3,4-epoxycyclohexylmethyl(meth)acrylate, 1,2-etyleneglycol glycidylether(meth)acrylate, 1,3-propyleneglycolglycidylether(meth)acrylate,1,4-butyleneglycolether (meth)acrylate,1,6-hexanediolether(meth)acrylate,1,3-(2-ethyl-2-butyl)-propanediolglycidylether(meth)acrylate and acrylicglycidyl ether and 99 to 5% mole of one or more monomers selected frommethyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate,n-butyl(meth)acrylate, isobutyl(meth)acrylate, tert.butyl(meth)acrylate,2-ethylhexyl(meth)acrylate, stearyl(meth)acrylate, tridecyl(meth)acrylate, cyclohexyl(meth)acrylate, n-hexyl(meth)acrylate,benzyl(meth)acrylate, phenyl(meth)acrylate, isobornyl(meth)acrylate,nonyl(meth)acrylate, hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, hydroxybutyl(meth)acrylate,1,4-butandiolmono (meth)acrylate, the esters of methacrylic acid, maleicacid, maleic anhydride, itaconic acid, dimethylaminoethyl(meth)acrylate,diethylaminoethyl(meth)acrylate, styrene, α-methylstyrene, vinyltoluene,(meth)acrylonitrile, vinylacetate, vinylpropionate, acryl-amide,methacrylamide, methylol(meth)acrylamide, vinylchloride, ethylene,propylene, C4-20 olefins and α-olefins.
 4. Composition according toclaim 1, wherein the carboxylic acid group containing acrylic copolymers(C) and (C′) are prepared from: 1 to 95% mole of at least one of acrylicacid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid,maleic acid, citraconic acid or the monoalkylesters of unsaturateddicarboxylic acids and 99 to 5% mole of one or more monomers selectedfrom methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate,n-butyl(meth)acrylate, isobutyl(meth)acrylate, tert.butyl(meth)acrylate,2-ethylhexyl(meth)acrylate, stearyl(meth)acrylate, tridecyl(meth)acrylate, cyclohexyl(meth)acrylate, n-hexyl(meth)acrylate,benzyl(meth)acrylate, phenyl (meth)acrylate, isobornyl(meth)acrylate,nonyl(meth)acrylate, hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, hydroxybutyl(meth)acrylate, 1,4-butandiolmono(meth)acrylate, the esters of methacrylic acid, maleic acid, maleicanhydride, itaconic acid, dimethylaminoethyl(meth)acrylate,diethylaminoethyl(meth)acrylate, styrene, α-methylstyrene, vinyltoluene,(meth)acrylonitrile, vinylacetate, vinylpropionate, acryl-amide,methacrylamide, methylol(meth)acrylamide, vinylchloride, ethylene,propylene, C4-20 olefins and α-olefins.
 5. Composition according toclaim 1 wherein the carboxylic acid group containing polyester (B) isamorphous and has: an acid number from 15 to 100 mg KOH/g and preferablyfrom 30 to 70 mg KOH/g. number averaged molecular weight ranging from1100 to 15000 and preferably from 1600 to 8500, measured by gelpermeation chromatography (GPC) an ICI cone and plate viscosityaccording to ASTM D4287-88, measured at 200° C. ranging from 5 to 15000mPa.
 6. Composition according to claim 1 wherein the carboxylic acidgroup containing polyester (B′) is semi-crystalline and has: an acidnumber from 15 to 100 mg KOH/g and preferably from 30 to 70 mg KOH/g anumber averaged molecular weight ranging from 1100 to 17000 andpreferably from 1400 to 11200 a fusion zone from 50 to 150° C., measuredby Differential Scanning Calorimetry (DSC) according to ASTM D3418 witha heating gradient of 20° C. per minute a glass transition temperature(Tg) from −50 to 40° C., measured by Differential Scanning Calorimetry(DSC) according to ASTM D3418 with a heating gradient of 20° C. perminute a degree of crystallinity, measured by Differential ScanningCalorimetry (DSC) according to ASTM D3415 of at least 5 J/g andpreferably at least 10 J/g an ICI (cone/plate) viscosity according toASTM D4287-88, measured at 100° C. of at least 100 mPa·s.
 7. Compositionaccording to claim 1 wherein the carboxylic acid group containingamorphous polyester (B) is obtained of from 50 to 100% mole ofterephthalic acid or isophthalic acid or their mixtures and from 0 to50% mole of at least one aliphatic, cycloaliphatic or aromatic polyaciddifferent from terephthalic acid or isophthalic acid, referring to thepolyacid constituents, and from 40 to 100% mole of neopentyl glycol andfrom 0 to 60% mole of at least one other aliphatic and/or cycloaliphaticpolyol, referring to the polyol constituents.
 8. Composition accordingto claim 1 wherein the carboxylic acid group containing semi-crystallinepolyester (B′) is obtained of from 70 to 100% mole of terephthalic acid,1,4-cyclohexanedicarboxylic acid and/or a linear chain dicarboxylic acidcontaining 4 to 16 carbon atoms and from 0 to 30% mole of at least oneother aromatic, aliphatic or cycloaliphatic polyacid, referring to thepolyacid constituents, and from 70 to 100% mole of at least onecycloaliphatic or linear chain aliphatic diol containing 2 to 16 carbonatoms and from 0 to 30% mole of at least one other aliphatic polyol,referring to the polyol constituents.
 9. Composition according to claim1 wherein the carboxylic acid group containing amorphous and/orsemi-crystalline polyester is linear or branched and/or comprisespolyanhydride end-capped groups.
 10. Composition according to claim 1wherein the thermosetting catalyst (D) is an amine, phosphine, ammoniumsalt, phosphonium salt, acid blocked amine or acid blocked phosphinecontaining compound and is present in an amount of from 0.1 to 5 weightpercent with respect to the weight of the total weight of (A), (A′),(B), (B′), (C) and (C′).
 11. Thermosetting powder coating compositionaccording to claim 1, containing at least one additive chosen fromUV-light absorbers and/or hindered amine light stabilisers, flow controlagents and degassing agents.
 12. A clear lacquer containing thethermosetting powder coating composition of claim
 11. 13. Thermosettingpowder coating composition of claim 11 containing pigments, dyes,fillers.
 14. Process for obtaining a low gloss coating on an article,wherein a thermosetting powder coating composition according to claim 1is applied to the said article by an electrostatic or friction chargingspray gun, or by the fluidised bed technique, and in that the articlethus coated is cured at a temperature of from 80 to 150° C. 15.(canceled)
 16. (canceled)
 17. Entirely or partially coated substrateusing the process of claim 14.